Metamorphism

Welcome to the ninth episode of the Petrology course! Building upon previous discussions on petrology, igneous, sedimentary, and metamorphic rocks, the rock cycle, magma, weathering, and diagenesis, this episode delves into the process of metamorphism itself. We will examine the agents of metamorphism – heat, pressure, and chemically active fluids – and how they cause changes in pre-existing rocks (the protolith) to create metamorphic rocks. The episode will cover different types of metamorphism, including contact, regional, and dynamic metamorphism, and the concept of metamorphic grade. Understanding metamorphism is crucial for interpreting Earth's history, as metamorphic rocks provide a record of the conditions and processes that have occurred deep within the Earth's crust and mantle.

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These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

What is metamorphism?

  1. The melting of rock to form magma.
  2. The breakdown of rock at the Earth's surface.
  3. The transformation of existing rocks without melting, due to changes in temperature, pressure, and/or fluids.
  4. The accumulation and consolidation of sediments.
  5. The cooling of magma.
  6. The study of fossils.

What are the primary agents of metamorphism?

  1. Wind, water, and ice.
  2. Heat, pressure, and chemically active fluids.
  3. Sunlight, gravity, and magnetism.
  4. Erosion, deposition, and compaction.
  5. Plants and animals
  6. Volcanism and earthquakes.

What is the difference between contact and regional metamorphism?

  1. Contact metamorphism occurs near magma intrusions, while regional metamorphism occurs over large areas due to mountain building.
  2. Contact metamorphism occurs at high pressures, while regional metamorphism occurs at high temperatures.
  3. Contact metamorphism produces foliated rocks, while regional metamorphism produces non-foliated rocks.
  4. Contact metamorphism only affects sedimentary rocks, while regional metamorphism only affects igneous rocks.
  5. There is no real difference.
  6. Contact metamorphism occurs near the surface while regional metamorphism occurs deeper.

What is metamorphic grade?

  1. The size of the crystals in a metamorphic rock.
  2. The intensity of metamorphism, reflecting temperature and pressure conditions.
  3. The type of protolith that was metamorphosed.
  4. The degree of weathering a metamorphic rock has experienced.
  5. The economic value.
  6. The color.

What are index minerals?

  1. Minerals that are always present in metamorphic rocks.
  2. Minerals that are used to determine the age of a metamorphic rock.
  3. Minerals that are stable under specific temperature and pressure conditions, indicating metamorphic grade.
  4. Minerals that are economically valuable.
  5. Minerals that are only found in igneous rocks.
  6. Minerals that have been weathered.

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